The glenoid cavity is located on the upper external boarder of the scapula between the acromion process and the coracoid, a bony formation know as the scapula head. The glenoid cavity is a shallow, pear-shaped articular surface whose longest diameter is from above downward and whose direction is outward and forward from the body. It is broader below than above, and at its apex there is a slight depression, the supra-glenoid tubercle, to which is attached is the long tendon of the biceps muscle. The cavity is covered with cartilage and its margins, slightly raised, give attachment to a fibro-cartilaginous structure, the glenoid ligament, by which the cavity is deepened.
The glenoid cavity articulates with a large, rounded head at the proximal end of the humerus, or upper arm bone. The head is nearly hemispherical in form and is directed upward, inward, and a little backward. Its surface is smooth and coated with cartilage.
By process of aging or disease, the glenoid cavity or the head of the humerus or both may degrade and it may be necessary to replace these natural structures with prostheses. Both glenoid and humeral prostheses are known. An exemplary structure is described in U.S. Pat. No. 4,964,865 Burkhead, Dale, and myself, which patent is assigned to the same assignee as my present invention. The patent also describes other glenoid/humeral prostheses which are presently available.
It is difficult to implant a glenoid or humeral prostheses accurately because of the constrained geometry of the shoulder joint. An incision exposing the joint should be as small as possible and trauma in manipulating the joint should be minimized. At the same time it is necessary to implant a humeral prosthesis accurately and firmly in the humerus so that integration of the prosthesis will integrate with the humeral bone, the prosthesis will not work its way out of the bone, and the articulating surfaces of the prosthesis will mate accurately with a glenoid or a glenoid prosthesis. It is sometimes necessary, also, to withdraw a humeral prosthesis out of the humerus.
With the foregoing in mind, it has been an object of my invention to provide any apparatus which attaches to a humeral prosthesis for implantation of the prosthesis into the humerus.
Another object of my invention is to provide an apparatus which can transmit the forces necessary for implanting a prosthesis without deforming that prosthesis.
It is also an object of my invention to provide an apparatus which makes it easy to control the angle of presentation of humeral prosthesis into the bone.
Another important object of my invention is to provide an apparatus which can withdraw a humeral prosthesis out of the humerus.